Hydraulic cyclones, jigs and heavy media cyclones are widely used apparatus for fine coal preparation. The average particle size of fine coal slurry having practical application can reach 0.01 mm, probably even 0.001 mm. Coal organic components and adhered inorganic mineral particles such as ferrous sulfide and silicon dioxide can be separated effectively by making ultra-fine coal particles. This enables coal further preparation. The separation mechanism of hydraulic cyclone is affected by particle size. That is to say, the effect of separation according to particle density will be affected by particle size. The particle minimum size for jigging and heavy media cycloning is 0.2 mm which makes it difficult to remove inorganic minerals. The settling velocity of particles in the slurry becomes very low under normal gravity when particles become fine. Particles settling may even stop due to interaction force between particles and disturbance caused by ultra-fine particles in the slurry. Therefore, conventional coal preparation equipment based on gravity effect doesn't work. A centrifugal jig has been disclosed in patent PCT/AU86/00016 published on Jul. 31, 1986. It was further improved in patent PCT/AU89/00279 published on Jan. 11, 1990 and patent PCT/AU98/00657 published on Feb. 25, 1999. The centrifugal jig presented in the patent series can separate fine particles with different density by using centrifugal acceleration of tens of gravity. This type of equipment is used to collect small particles of large density by discharging small particles through the screen. However, the preparation of fine coal slurry aims at removing mineral particles of high density and remaining particles of low density.